To provide fuel to a combustion chamber of an internal combustion engine, which may be described as an injection event, a fuel injector receives a drive profile signal from a controller of the engine to produce a “rate shape” of the fuel injection. Depending on the engine operating conditions, the rate shapes to be delivered to the combustion chamber by the fuel injector during an injection event can be varied (e.g., the fuel injector may be controlled to provide a trapezoid shape, a square shape, or a boot shape injection profile to name a few).
By varying the Piezo voltage profile (i.e., the control input or drive profile signal characteristics), the needle position of the fuel injector can be varied to inject a desired rate shape of the fuel injection to the combustion chamber. Regulating needle position to achieve a specified rate shape within a tight tolerance presents challenges in open-loop operation. Imprecise rate shapes result generally in undesirable engine performance (i.e., reduced fuel efficiency and increased emissions output). Therefore, a within the injection cycle closed-loop technique (“within-cycle”) was developed and disclosed in PCT Patent Application No. PCT/US2014/55856, filed Sep. 16, 2014, entitled “SYSTEM FOR ADJUSTING A FUEL INJECTOR ACTUATOR DRIVE SIGNAL DURING A FUEL INJECTION EVENT” (hereinafter referred to as “the Within-Cycle Application”), the entire disclosure of which being expressly incorporated herein by reference. While the teachings of the Within-Cycle Application improve the accuracy of fuel injection events to a large extent (i.e., in terms of matching the actual rate shape to the desired rate shape), the closed-loop system performance of the fuel injectors is still adversely affected by the time delay between the output rate shape and the measured sense signal(s) used to produce the output. In general, because of this time delay, the within-cycle techniques alone still permit some error between the desired rate shape and the actual rate shape of the fuel injection profile.